This invention pertains generally to the art of methods and apparatuses for measuring and analyzing uniformity characteristics of tires, and more specifically to the measurement and analysis of radial and lateral forces using the waveforms of the forces and the first and second derivatives of those waveforms.
Conventional uniformity machine measurements and calculations depict the tire uniformity characteristics in terms of peak-to-peak amplitudes and spectral components for radial, lateral, and tangential forces. Plysteer, conicity, bulge, and valley radial and lateral runouts are also included.
Production tires are screened by uniformity machines, and the measured and calculated information is then compared to original equipment manufacturer's (OEM) specifications for a pass or fail sorting.
Ride testing indicates that its possible for tires to pass all OEM specifications and still cause rough ride and other undesirable vehicle effects.
The peak-to-peak amplitude of the above-mentioned parameters is important, but the rate of change of these parameters is also important. The rate of change of these parameters may be defined by the first and second derivatives with respect to time of these measured parameters.
Peak-to-peak variations may be within specifications, but the rate of change of these parameters can be very localized and cause instantaneous changes in velocity and acceleration. Today's sensitive automobile suspensions can pick up and transmit the localized changes through the vehicle. Additionally, while grinding of the offending tire may lower the peak-to-peak measurements of the above-mentioned parameters, grinding may not eliminate the high rates of change of the forces. In such case the tire may still produce an unacceptable ride.
U.S. Pat. No. Re. 28,775 to Tarpinian et al. discloses the use of force harmonics to mark tires.
U.S. Pat. No. 4,258,567 to Fisher, III is directed to the use of force data to identify sidewall deformity in tires.
U.S. Pat. No. 5,313,827 to Yovichin is directed to the use of runout measurements to identify sidewall deformity in tires.
U.S. Pat. No. 3,894,421 to Sperberg and U.S. Pat. No. 4,938,056 to DeRudder et al. disclose the measurement of pneumatic pressure in tires to detect uniformity problems.
The present invention contemplates a new and improved method for analyzing tire uniformity which is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results.